1. Field of the Invention
The present invention relates to a micromirror device for an image display apparatus by which it is possible to convert the traveling path of incident light, and more particularly, to a micromirror device for an image display apparatus by which it is possible to convert the traveling path of incident light by rotating a mirror.
2. Description of the Related Art
In general, a micromirror device for an image display apparatus includes a plurality of mirrors installed to be driven by an electrostatic force and reflects incident light at a predetermined angle. The micromirror device is applied to a light scanning apparatus such as an image display apparatus of a projection television, a scanner, a photo copier, and a facsimile machine. In particular, when the micromirror device is used as the image display apparatus, as many mirrors as there are pixels are two-dimensionally arranged and light is reflected by driving the respective mirrors according to a video signal with respect to the respective pixels, thus controlling the brightness.
Referring to FIG. 1, a conventional micromirror device includes a substrate 1, an elastic plate 5 and a mirror 8 separated from each other in a vertical direction with respect to the substrate 1 by first and second posts 3 and 7, and a light shielding plate 6 positioned on the elastic plate 5 around the mirror 8 for shielding the progress of the incident light.
An electrode 2 is formed on the substrate 1. The electrode 2 lifts the mirror 8 by mutual electrostatic attraction between the electrode 2 and the elastic plate 5. The elastic plate 5 is supported by the first post 3 and is located in a predetermined position on the substrate 1. The elastic plate 5 includes a horizontal unit 5a which directly contacts the first post 3 and maintains a horizontal state, and an elastic unit 5b for supporting the second post 7 and lifted in a vertical direction by the mutual electrostatic attraction according to the on and off states of the, electrode 2. The mirror 8 is arranged on the elastic unit 5b by the second post 7 and is lifted in a vertical direction as the elastic unit 5b is lifted. The light shielding plate 6 is installed on the horizontal unit 5a of the elastic plate 5 so as to be arranged around the mirror 6.
The conventional micromirror device having the above structure converts the traveling path of the incident light by the principle shown in FIGS. 2 and 3.
FIG. 2 schematically shows a micromirror device in which there is an electric potential difference between the electrode 2 and the elastic plate 5. As shown in FIG. 2, since the elastic plate 5 is tilted toward the electrode 2 due to the electrostatic attraction, the restoring force of the elastic plate 5 becomes large. The elastic unit 5b falls down to a position in which the restoring force is equal to the electrostatic attraction. Accordingly, the mirror 8 arranged on the elastic unit 5b falls down toward the electrode 2. Since the light shielding plate 6 is positioned on the horizontal unit 5a, the vertical height thereof is maintained. Therefore, the light shielding plate 6 protrudes around the mirror, thus shielding the light L incident on the mirror 8 to be inclined and reflected from a reflection surface of the mirror 8 without letting the light L be incident on a projection lens 10 arranged on a reflection path.
FIG. 3 schematically shows a micromirror device when the electrostatic attraction is removed between the electrode 2 and the elastic plate 5. As shown in FIG. 3, the elastic unit 5b has the same height as that of the horizontal unit 5a due to the restoring force. In this case, the mirror 8 is lifted to have a height equal to the upper end of the light shielding plate 6. Therefore, the light L incident on the mirror 8 to be inclined and reflected from the reflection surface thereof is incident on the projection lens 10 arranged on the light path without the affection of the light shielding plate 6.
The micromirror device operates as described with reference to FIGS. 2 and 3. Accordingly, the brightness of the light facing the projection lens is determined by the respective pixels. Since the brightness is determined by the light shielding in the conventional micromirror device having the above structure, the angle of the incident light should be about 80xc2x0 or more. Therefore, an optical system such as a projection lens is difficult to arrange. Also, since the light incident on the end of the light shielding plate is diffracted, screen contrast deteriorates due to the light. When such a micromirror device is used for the display apparatus, it is difficult to arrange the heights of a plurality of light shielding plates to be uniform to correspond to all the pixels having a two-dimensional array structure.
To solve the above problem, it is an objective of the present invention to provide a micromirror device by which it is possible to convert a traveling path of incident light due to the rotation of mirrors by improving the structure of a horizontal supporting plate.
Accordingly, to achieve the above objective, there is provided a micromirror device for an image display apparatus, comprising a substrate, a pair of first posts protrusively formed on an upper surface of the substrate so as to be separated from each other by a predetermined distance, electrodes formed on the substrate, a supporting plate supported by the first posts and rotatably arranged using a portion supported by the first posts as a hinge point, a second post protrusively formed on the supporting plate, and a mirror supported by the second post for reflecting light incident on one surface thereof, wherein a slope of the mirror can be controlled by an electrostatic attraction between the electrode and the mirror.